1. Field of the Invention
The present invention relates to a low temperature waste crushing system for crushing waste tire, plastics, etc., by taking advantage of cold shortness, specifically a system effectively utilizing a cascaded refrigerating system.
2. Description of the Related Art
A crushing method taking advantage of cold shortness in which iron and steel materials, etc., are cooled by, for example, very low temperature cooling medium such as liquid nitrogen below their cold shortness transition temperature to reduce them to a brittle state like glass, and crushed, is disclosed in Japanese Unexamined Patent publication No. Sho 51-39452.
Similarly, in the case of waste tire and plastics and the like, it is enough to cool them below their cold shortness transition temperatures which are about xe2x88x9270xc2x0 C.xcx9cxe2x88x9275xc2x0 C. for crushing Presently, almost all of the cooling method adopted is to cool them to a very low temperature by spraying liquid nitrogen (xe2x88x92196xc2x0 C.) on them before crushing.
The conventional crushing system at low temperature using the low temperature liquid nitrogen is shown in FIG. 3. It is composed of a material supplying section 50, a heat sink for supplying liquid nitrogen, a liquid nitrogen freezer 52 in which the material 50a of about 20xc2x0 C. supplied from the material supplying section 50 is cooled to be reduced to the frozen material 52a of about xe2x88x92130xc2x0 C. by spraying with liquid nitrogen 51a of about xe2x88x92196xc2x0 C. supplied from the heat sink 51, and a crushing section 53 in which crushed product 53a of about xe2x88x9275xc2x0 C. is obtained by crushing the frozen material 52a. 
In the liquid nitrogen freezer 52, liquid nitrogen is sprayed on the material 50a and the nitrogen gas gasified through spraying is exhausted to the atmosphere by an exhaust blower or the like not shown in the drawing. In the crushing section 53, the frozen material 52a of about xe2x88x92130xc2x0 C. is raised in temperature by the heat generated at crushing to be reduced to the crushed product 53a of about xe2x88x9275xc2x0 C.
The conventional method using liquid nitrogen, has the advantage that liquid nitrogen is comparatively cheap and easy to handle. However, it has a problem which makes it not the best system for environmental hygiene because the nitrogen gas used for freezing the waste material for low temperature crushing is exhausted to the atmosphere. Further, in the case liquid nitrogen is used, there is a problem that a stepwise cooling of high efficiency is not possible and that a heat sink of xe2x88x92196xc2x0 C. is used for obtaining a frozen material of about xe2x88x9275xc2x0 C. or lower which is the glass transition temperature of the material.
Moreover, a cooling mechanism for absorbing the heat generated in crushing is not provided at the crushing section Thus, the frozen material is heated at crushing, and necessitates a setting and securing of the frozen temperature which takes the change of quality of the material due to temperature rise at the crushing into consideration.
To solve these problems of the prior art, an art is disclosed in Japanese Unexamined Patent Publication No. Hei 7-88461. Here, a system for crushing waste household electrical appliances and the like at low temperature by utilizing refrigeration is shown. Firstly, liquid nitrogen is supplied from the lower temperature side and lumps of metal are cooled to below xe2x88x92100xc2x0 C. by the latent and sensible heat of liquid nitrogen. Then plastic materials are cooled to xe2x88x9240xc2x0 C. by the sensible heat of the gasified nitrogen. Further, the flon used for flon refrigerating cycle is cooled to xe2x88x9220xc2x0 C. by the sensible heat of the nitrogen gas after cooling the plastic materials, and the nitrogen gas having finished cooling is introduced to a crushing device to be used as anti-explosion purge gas.
However, also in this prior art, the nitrogen gas used for freezing for crushing at a low temperature is finally exhausted to the atmosphere. Therefore, as is the case with the aforementioned art, this prior art can not be said to be a superior system from the viewpoint of environmental hygiene.
The present invention was made in light of the problems mentioned above, and an object is to provide a low temperature crushing system without using liquid nitrogen, which reduces burden to the environment in comparison with the prior art of cooling with liquid nitrogen.
Another object of the present invention is to provide a crushing system at freezing low temperature, which enables bringing efficiency to cooling by adopting stepwise cooling along with effective removal of the heat generated at crushing.
The present invention is a low temperature crushing system having a low temperature freezing section, for cooling material below its cold shortness transition temperature (glass transition temperature at which low-temperature embrittlement occurs) by receiving the supply of refrigeration from a heat sink and a crushing section for crushing the material cooled in the low temperature freezing section by taking advantage of cold shortness, and characterized in that
the heat sink is configured as a binary refrigerating cycle combining two different refrigeration cycles, the first refrigerating cycle for obtaining the first refrigeration (hereinafter referred to as higher temperature refrigeration) higher in temperature than the cold shortness transition temperature and the second refrigerating cycle for obtaining the second refrigeration (hereinafter referred to as lower temperature refrigeration) lower in temperature than the cold shortness transition temperature,
the low temperature freezing section is configured as a dual step cooling section, the preceding and succeeding step, each of which received refrigeration of different temperatures, and
the preceding step of the dual step cooling section is supplied with the higher temperature refrigeration of the first refrigerating cycle and the succeeding step is supplied with the lower temperature refrigeration of the second refrigerating cycle.
The binary refrigerating cycle is preferably configured as a cascaded binary refrigerating cycle combining two different cycles, the first refrigerating cycle for obtaining the higher temperature refrigeration and the second refrigerating cycle for obtaining the lower temperature refrigeration by introducing the higher temperature refrigeration to its condenser.
Further preferably, the cascaded binary refrigerating cycle comprises a higher temperature condensing unit configured as the first refrigerating cycle which uses ammonia as a refrigerant and a lower temperature condensing brine unit configured as the second refrigerating cycle which uses a refrigerant of hydrocarbon group such as ethane and methane,
the higher temperature condensing unit supplies a part of the latent heat of vaporization of ammonia refrigerant to the load of the preceding step of the dual step cooling section and at the same time introduces the remainder to the condensing part of the lower temperature condensing brine unit to make the condensing part a cascade condenser, and
the lower temperature condensing brine unit supplies to the load of the succeeding step of the dual step cooling section the low temperature brine cooled in a brine cooler to which the ethane refrigerant condensed in the cascade condenser is supplied.
The two step cooling section suitably comprises:
a pre-cooling room in which the waste material is pre cooled by the first cooling air which is produced by supplying the higher temperature refrigeration of the first refrigerating cycle to the air cooler of the preceding step and is higher in temperature than the cold shortness transition temperature; and
a lower temperature cooling room in which the pre-cooled waste material is cooled to a temperature lower than the cold shortness transition temperature by the second cooling air which is produced by supplying the lower temperature refrigeration to the air cooler of the succeeding step and is lower in temperature than the cold shortness transition temperature.
Further preferably, the dual step cooling section comprises:
a transfer belt for transferring waste material, and nozzles for forming air jet provided above the belt along the direction of the transfer and divided in preceding and succeeding group along the direction of transfer; a plurality of air coolers for cooling the air to be supplied to each group of nozzles; and a tunnel covering these; and
the dual step cooling freezer is so configured that the higher temperature refrigeration is supplied to the air cooler which supplies the air to the preceding group of the nozzles and the lower temperature refrigeration to the air cooler which supplies the air to the succeeding group of the nozzles.
The crushing section is suitably provided with a crushing machine in which the frozen waste material is crushed while removing the heat generated at crushing through blowing the air of low temperature below the cold shortness transition temperature produced by the lower temperature refrigeration into the crushing machine.
Hereinbelow, the present invention will be described in a concrete manner.
With refrigerant such as ammonia and the like generally used in a conventional refrigerating cycle, as the specific volume of evaporated vapor is very large when the evaporation temperature is about xe2x88x9270xc2x0 C. and below, the use of refrigerant such as methane, ethane, and the like whose specific volume of saturated vapor is small becomes necessary. However, sufficient refrigerating effect and capacity can not be obtained with the refrigerating cycle using only these refrigerants. With this being the situation, the present invention is configured as a binary refrigerating cycle, in which the higher temperature side refrigerating cycle uses a generally used refrigerant with a high refrigerating capacity, more specifically, ammonia refrigerant to condense the compressed refrigerant gas (ethane) in the lower temperature side refrigerating machine and heat exchange is performed between the evaporator of the higher temperature side refrigerating machine and the condenser of the lower temperature side refrigerating machine in the cascade condenser to condense the lower temperature side refrigerant.
Thus, the higher temperature is efficiently obtained by the first refrigerating cycle using generally used refrigerant such as ammonia and the like, and the lower temperature refrigeration is obtained by the second refrigerating cycle using refrigerant such as methane, ethane, and the like whose specific volume of saturated vapor is small. With the dual step cooling by the higher temperature refrigeration and the lower temperature refrigeration, the cooling load of the lower temperature side is lightened.
Particularly, the present invention uses the binary refrigerating cycle instead of conventional cooling and freezing by releasing liquid nitrogen, and cools the waste material stepwise to the cold shortness transition temperature by the air cooled by heat exchange. As cooled air is used as coolant for cooling waste material, the coolant can be exhausted in an as-is status without any harm to the environment. Cooling to the cold shortness transition temperature of below xe2x88x9270xc2x0 C. is possible, although air which holds substantially small cold energy compared with liquid nitrogen is used, for the configuration of dual step cooling is adopted, which is made possible by the use of the binary refrigerating cycle.
Further particularly, the heat sink of the present invention is configured so that ammonia refrigerant whose evaporation temperature is high, is used in the first refrigerating cycle to obtain the higher temperature refrigeration; and hydrocarbon group refrigerants such as ethane, methane, and the like are used for the second refrigerating cycle to obtain the lower temperature refrigeration.
In the second refrigerating cycle for obtaining the lower refrigeration, direct heat exchange between cooling air and/or waste material is not done. Instead, HFE (hydrofluoroether), a highly safe, nonflammable inactive liquid of fluorine group, having small earth-warming effect with zero ozone destroying coefficient and short life in the air, is used as brine and the low temperature cooling is performed by the brine
Thus, the danger of the inflammation of ethane and the like is excluded when crushing the waste material of the temperature below its cold shortness transition point in the crushing section
Although ammonia refrigerant is used, as the pre-cooling of the waste material is performed by the air produced through heat exchange with the ammonia refrigerant, the configuration of the hermetically sealed refrigerating cycle is possible without the danger of ammonia leak, which is very desirable for the environment.
Thus, the present invention is configured as the following: a part of the latent heat of evaporation of the first refrigerating cycle unit for obtaining the higher temperature of refrigeration is introduced to the preceding cooling step for pre-cooling the waste material in the tunnel type freezer; the rest of the latent heat of evaporation is introduced to the condenser part of the lower temperature side condensing brine unit which is the second refrigerating cycle for obtaining the lower temperature refrigeration. Hereby, the cascade condenser is formed and the high pressure, high temperature ethane refrigerant is condensed. Lowe temperature brine of HFE, an inactive liquid, is obtained by the medium of the condensed ethane. This low temperature brine is used as a lower temperature heat sink at the succeeding cooling step of the dual step cooling section, as well as for cooling the air to be used for removing the heat generated at the crushing.
By the configuration of the dual step, the tunnel type freezer as set forth in claim 1 is composed of the pre-cooling room formed in the preceding step and the lower temperature cooling room formed in the succeeding step, and so the cooling load of the lower temperature cooling in the succeeding step is lightened by the pre-cooling.
The crushing section is so configured that the crushing is performed while removing the heat generated at crushing by blowing on the waste material the cold air which is lower in temperature than the cold shortness transition temperature and produced through the medium of the lower temperature heat sink. By blowing the cold air lower in temperature than the cold shortness transition temperature in the crushing process, the removal of the heat generated at crushing and the fracture in low temperature are promoted, and welding of the crushed material and deterioration of the material due to the heat generated at crushing are also prevented.
It is preferable for the removal of the heat generated at crushing to cool the jacket of the crushing section in addition to blow the cold air in the crushing machine.